I had the same problem with my vox. Here's what I ended up doing since mine was no longer covered by warranty.

1) Take off the back and remove the battery.
2) Take out all the screws and remove the plastic case cover.
3) Find the SD card and remove it
4) Boot up a computer in to Linux. I used my laptop as it has Ubuntu but you could just download the Ubuntu live cd and boot any computer.
5) Find in this forum where to download update.zip. Kobo has made it available to download.
6) copy update.zip into the largest partition on the SD card (you need to have a USB card reader or like that)
7) unmount the sd card from ubuntu and put it back in the vox.
8) plug in the battery and hold the volume + and power button. It should take at least 2 to 5 minutes to apply the update. Once it updates and reboots it should give you the setup screen. At this point you should let it complete it's update check and such before putting it back together.

It's been a few months since I've had to do this so it's possible that you may need to copy it to one of the other partitions on the sd card. I think mine had 4 partitions but most where not big enough to hold the zip file. Also do not unzip the contents of the update.zip file. Just leave it as is and copy it all to the partition. Finally you'll notice that I didn't reassemble the vox until I got it to the setup screen. This is because I wasn't sure about which partition to put the update.zip and didn't want to have take it all apart again.